This study will examine the relationship of drug side effects to the daily functioning of elderly ambulatory patients receiving care in the primary care practice of a teaching hospital. The study will test two hypotheses: (a) that drug side effects lead to diminished functioning, particularly in extended mobility and social activities and (b) that a strong patient/provider relationship characterized by high levels of communication and close monitoring of drug regimens will lessen the number and degree of side effects and thus lessen decrements in functioning. A telephone interview will be conducted with 800 patients sampled randomly from persons aged 65 and over who attend the practice; data will be obtained on use of prescribed and non-prescribed drugs, adherence to regimens, side effects experienced, interactions with clinicians, and functional capacity, as well as socio-demographic characteristics and use of health services. These data will be supplemented by medical record abstracts. In-person interviews will be carried out with the clinicians staffing the practice (residents, nurse practitioners, attending physicians) with regard to their prescribing, patient education and drug regimen monitoring procedures. A protocol for assessing the relationship between specific drugs and symptoms will be used to differentiate between side effects and signs/symptoms of disease processes. The functional decrements most likely to be affected by drug side effects are expected to be mobility within the home and community, and interactions with other people. There is evidence that maintenance of social activity levels is significant in resistance to disease, recovery following acute illness, and adjustment to limitations due to chronic diseases. The study will provide important information on drug use and prescribing patterns, and on the factors which influence the effects of drugs on functioning. Further, the findings will provide an understanding of an area increasingly important for the expanding elderly population, and a basis for possible targetted intervention studies.